U.S. patent application number 14/380106 was filed with the patent office on 2015-01-15 for composition for forming n-type diffusion layer, method for producing semiconductor substrate having n-type diffusion layer, and method for producing solar cell element.
The applicant listed for this patent is Hitachi Chemical Company, Ltd.. Invention is credited to Toranosuke Ashizawa, Mitsunori Iwamuro, Yasushi Kurata, Yoichi Machii, Takeshi Nojiri, Akihiro Orita, Tetsuya Sato, Mari Shimizu, Masato Yoshida.
Application Number | 20150017754 14/380106 |
Document ID | / |
Family ID | 49005447 |
Filed Date | 2015-01-15 |
United States Patent
Application |
20150017754 |
Kind Code |
A1 |
Sato; Tetsuya ; et
al. |
January 15, 2015 |
COMPOSITION FOR FORMING N-TYPE DIFFUSION LAYER, METHOD FOR
PRODUCING SEMICONDUCTOR SUBSTRATE HAVING N-TYPE DIFFUSION LAYER,
AND METHOD FOR PRODUCING SOLAR CELL ELEMENT
Abstract
The invention provides composition for forming an n-type
diffusion layer, the composition comprising a compound containing a
donor element, a dispersing medium, and an organic filler; a method
for producing a semiconductor substrate having an n-type diffusion
layer; and a method for producing a photovoltaic cell element.
Inventors: |
Sato; Tetsuya; (Tsukuba-shi,
JP) ; Yoshida; Masato; (Tsukuba-shi, JP) ;
Nojiri; Takeshi; (Tsukuba-shi, JP) ; Ashizawa;
Toranosuke; (Hitachi-shi, JP) ; Kurata; Yasushi;
(Tsukuba-shi, JP) ; Machii; Yoichi; (Tsukuba-shi,
JP) ; Iwamuro; Mitsunori; (Tsukuba-shi, JP) ;
Orita; Akihiro; (Tsukuba-shi, JP) ; Shimizu;
Mari; (Tsukuba-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hitachi Chemical Company, Ltd. |
Chiyoda-ku, Tokyo |
|
JP |
|
|
Family ID: |
49005447 |
Appl. No.: |
14/380106 |
Filed: |
January 10, 2013 |
PCT Filed: |
January 10, 2013 |
PCT NO: |
PCT/JP2013/050305 |
371 Date: |
August 21, 2014 |
Current U.S.
Class: |
438/57 ;
252/519.32; 438/563 |
Current CPC
Class: |
Y02E 10/547 20130101;
Y02P 70/521 20151101; H01L 31/1864 20130101; C03C 3/097 20130101;
C03C 8/08 20130101; Y02P 70/50 20151101; C08L 1/28 20130101; H01L
31/1804 20130101; H01L 31/022425 20130101; C03C 8/16 20130101; H01L
31/068 20130101; H01L 21/2225 20130101; H01L 21/2255 20130101; H01L
21/324 20130101 |
Class at
Publication: |
438/57 ;
252/519.32; 438/563 |
International
Class: |
H01L 21/225 20060101
H01L021/225; H01L 31/18 20060101 H01L031/18; H01L 21/324 20060101
H01L021/324 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 23, 2012 |
JP |
2012-037384 |
Claims
1. A composition for forming an n-type diffusion layer, the
composition comprising a compound containing a donor element, a
dispersing medium, and an organic filler.
2. The composition for forming an n-type diffusion layer according
to claim 1, wherein the organic filler is in a form of particles
having an average particle size of 10 .mu.m or less.
3. The composition for forming an n-type diffusion layer according
to claim 1, wherein the degradation temperature of the organic
filler is 700.degree. C. or less.
4. The composition for forming an n-type diffusion layer according
to claim 1, wherein the compound containing a donor element is a
compound containing phosphorus.
5. The composition for forming an n-type diffusion layer according
to claim 1, wherein the compound containing a donor element is in a
form of glass particles.
6. The composition for forming an n-type diffusion layer according
to claim 5, wherein the glass particles comprise at least one
substance containing a donor element selected from the group
consisting of P.sub.2O.sub.3 and P.sub.2O.sub.5, and at least one
glass component substance selected from the group consisting of
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3.
7. The composition for forming an n-type diffusion layer according
to claim 5, wherein a content of the glass particles in the
composition for forming an n-type diffusion layer is from 1 mass %
to 80 mass %.
8. The composition for forming an n-type diffusion layer according
to claim 6, wherein a content of the at least one substance
containing a donor element selected from the group consisting of
P.sub.2O.sub.3 and P.sub.2O.sub.5 in the glass particles is from
0.01 mass % to 10 mass %.
9. The composition for forming an n-type diffusion layer according
to claim 1, wherein a content of the organic filler in the
composition for forming an n-type diffusion layer is from 1 mass %
to 50 mass %.
10. A method for producing a semiconductor substrate having an
n-type diffusion layer, the method comprising: a process of
applying the composition for forming an n-type diffusion layer
according to claim 1 onto at least a part of a semiconductor
substrate; and a process of forming an n-type diffusion layer in
the semiconductor substrate by performing a heat treatment.
11. A method for producing a photovoltaic cell element, the method
comprising: a process of applying the composition for forming an
n-type diffusion layer according to claim 1 onto at least a part of
a semiconductor substrate; a process of forming an n-type diffusion
layer in the semiconductor substrate by performing a heat
treatment; and a process of forming an electrode on the n-type
diffusion layer.
Description
TECHNICAL FIELD
[0001] The present invention relates to a composition for forming
n-type diffusion layer, a method for producing a semiconductor
substrate having an n-type diffusion layer, and a method for
producing a solar cell element.
BACKGROUND ART
[0002] A conventional method for producing a silicon photovoltaic
cell element (a photovoltaic cell element) will be described below.
First, a p-type semiconductor substrate, in which a textured
structure is formed on a light-receiving surface in order to
increase efficiency by promoting a light trapping effect, is
prepared. Next, an n-type diffusion layer is uniformly formed by
performing a treatment in an atmosphere of a mix gas of phosphorus
oxychloride (POCl.sub.3), nitrogen and oxygen, at from 800 C to 900
C for several tens of minutes. In this conventional method, an
n-type diffusion layer is formed not only at a top surface but also
at side surfaces and a back surface, because phosphorus diffusion
is performed with a mix gas. Therefore, a side etching step needs
to be performed in order to remove the n-type diffusion layer
formed at side surfaces. Further, the n-type diffusion layer formed
at the back side needs to be converted to a p.sup.+-type diffusion
layer. For this purpose, an aluminum paste containing aluminum,
which is a group 13 element, is applied onto the n-type diffusion
layer formed at the back surface and a thermal treatment is
performed, whereby the n-type diffusion layer is converted to a
p.sup.+-type diffusion layer by diffusion of aluminum and an ohmic
contact is also established.
[0003] Further, a method of forming an n-type diffusion layer by
applying a solution containing a phosphate such as ammonium
dihydrogen phosphate (NH.sub.4H.sub.2PO.sub.4) has been proposed
(see, for example, Japanese Patent Application Laid-Open (JP-A) No.
2002-75894). However, even in this method, a phosphorus compound
diffuses from the region at which the solution has been applied
during a thermal treatment. As a result, a donor element is not
diffused in a selective manner and an n-type diffusion layer is
formed over the entire surfaces.
[0004] In connection with the above, a method for producing a
photovoltaic cell element, in which an n-type diffusion layer is
formed only at a specific region without forming unnecessary n-type
diffusion layers at side and back surfaces of a semiconductor
substrate, has been proposed (see, for example, International
Publication No. WO11/090,216). In this method, an n-type diffusion
layer is formed by applying a composition for forming an n-type
diffusion layer that contains glass particles including a donor
element, and a dispersing medium, onto a semiconductor substrate
and performing a thermal treatment.
[0005] As a structure of a photovoltaic cell element that attains a
higher conversion efficiency, a selective emitter structure, in
which a diffusion concentration of a donor element (hereinafter,
also referred to as a "diffusion concentration") at a region other
than a region immediately beneath an electrode is lower than that
at the region immediately beneath an electrode, has been known
(see, for example, L. Debarge, M. Schott, J. C. Muller, and R.
Monna, Solar Energy Materials & Photovoltaic cells, 74 (2002)
71-75). In this structure, since a region having a higher diffusion
concentration is formed at a region immediately beneath an
electrode (hereinafter, also referred to as a "selective emitter")
is formed, the contact resistance between an electrode and a
semiconductor substrate can be reduced. Further, since the
diffusion concentration at a region other than the region at which
an electrode is formed is relatively low, the conversion efficiency
of a photovoltaic cell element can be improved. In order to obtain
a selective emitter structure, it is required to form an n-type
diffusion layer in the form of a fine line having a width of within
several hundred micrometers (approximately from 50 .mu.m to 250
.mu.m).
SUMMARY OF THE INVENTION
Technical Problem
[0006] In a case of a composition for forming an n-type diffusion
layer described in WO 11/090,216, a desired width of a line tends
not to be obtained due to expansion thereof, even when the
composition for forming an n-type diffusion layer is applied onto a
semiconductor substrate in a shape of a fine line. If the viscosity
is increased by changing the content of a dispersing medium in
order to overcome this problem, the composition tends to become
hard to handle and unable to be applied to a semiconductor
substrate.
[0007] The invention has been accomplished in view of these
conventional problems, and aims to provide a composition for
forming an n-type diffusion layer that is capable of forming a
fine-line n-type diffusion layer while suppressing expansion of the
line width, a method for producing a semiconductor substrate having
an n-type diffusion layer, and a method for producing a
photovoltaic cell element.
Solution to Problem
[0008] The means for solving the problem are as follows.
<1> A composition for forming an n-type diffusion layer, the
composition comprising a compound containing a donor element, a
dispersing medium, and an organic filler. <2> The composition
for forming an n-type diffusion layer according to <1>,
wherein the organic filler is in a form of particles having an
average particle size of 10 .mu.m or less. <3> The
composition for forming an n-type diffusion layer according to
<1> or <2>, wherein the degradation temperature of the
organic filler is 700 C or less. <4> The composition for
forming an n-type diffusion layer according to any one of <1>
to <3>, wherein the compound containing a donor element is a
compound containing phosphorus. <5> The composition for
forming an n-type diffusion layer according to any one of <1>
to <4>, wherein the compound containing a donor element is in
a form of glass particles. <6> The composition for forming an
n-type diffusion layer according to <5>, wherein the glass
particles comprise at least one substance containing a donor
element selected from the group consisting of P.sub.2O.sub.3 and
P.sub.2O.sub.5, and at least one glass component substance selected
from the group consisting of SiO.sub.2, K.sub.2O, Na.sub.2O,
Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5,
SnO, ZrO.sub.2 and MoO.sub.3. <7> The composition for forming
an n-type diffusion layer according to <5> or <6>,
wherein a content of the glass particles in the composition for
forming an n-type diffusion layer is from 1 mass % to 80 mass %.
<8> The composition for forming an n-type diffusion layer
according to any one of <5> to <7>, wherein a content
of the at least one substance containing a donor element selected
from the group consisting of P.sub.2O.sub.3 and P.sub.2O.sub.5 in
the glass particles is from 0.01 mass % to 10 mass %. <9> The
composition for forming an n-type diffusion layer according to any
one of <1> to <8>, wherein a content of the organic
filler in the composition for forming an n-type diffusion layer is
from 1 mass % to 50 mass %. <10> A method for producing a
semiconductor substrate having an n-type diffusion layer, the
method comprising: a process of applying the composition for
forming an n-type diffusion layer according to any one of <1>
to <9> onto at least a part of a semiconductor substrate; and
a process of forming an n-type diffusion layer in the semiconductor
substrate by performing a heat treatment. <11> A method for
producing a photovoltaic cell element, the method comprising: a
process of applying the composition for forming an n-type diffusion
layer according to any one of <1> to <9> onto at least
a part of a semiconductor substrate; a process of forming an n-type
diffusion layer in the semiconductor substrate by performing a heat
treatment; and a process of forming an electrode on the n-type
diffusion layer.
Advantageous Effect of the Invention
[0009] According to the invention, it is possible to provide a
composition for forming an n-type diffusion layer that is capable
of forming a fine-line n-type diffusion layer while suppressing
expansion of the line width, a method for producing a semiconductor
substrate having an n-type diffusion layer, and a method for
producing a photovoltaic cell element.
BRIEF DESCRIPTION OF DRAWINGS
[0010] FIG. 1 is a conceptual cross-sectional view showing an
example of the processes for producing a photovoltaic cell element
according to the present embodiment.
[0011] FIG. 2 is a plan view of a photovoltaic cell element viewed
from the top surface side according to the embodiment.
[0012] FIG. 3 is an enlarged perspective view of a part of FIG.
2.
DESCRIPTION OF EMBODIMENTS
[0013] In the present specification, the term "process" includes
herein not only an independent process, but also a process that
cannot be clearly distinguished from other processes, insofar as an
intended function of the process can be attained. A numerical range
expressed by "from x to y" includes x and y as the minimum and
maximum values, respectively. When there are plural substances that
correspond to a component of a composition, the content of the
component refers to a total of the plural substances in the
composition, unless otherwise specified. The term "content" refers
to a percentage by mass with respect to 100 mass % of the
composition for forming an n-type diffusion layer, unless otherwise
specified.
[0014] <Composition for Forming n-Type Diffusion Layer>
[0015] The composition for forming an n-type diffusion layer
according to the invention includes a compound containing a donor
element, a dispersing medium, and an organic filler. As necessary,
the composition may include other additives in view of application
suitability and the like. The composition for forming an n-type
diffusion layer refers to a material that includes a donor element
and is capable of forming an n-type diffusion layer by thermally
diffusing the donor element after applying the composition onto a
semiconductor substrate. Since the composition for forming an
n-type diffusion layer according to the invention includes a
composition containing a donor element and an organic filler, it
can form an n-type diffusion layer only at a desired region without
forming an n-type diffusion layer at a region at which an n-type
diffusion layer is not to be formed. In addition, in a case in
which the n-type diffusion layer is a fine line, it is possible to
form an n-type diffusion layer while suppressing expansion of the
line width.
[0016] Consequently, in a case of production of a conventional
photovoltaic cell element to which the composition for forming an
n-type diffusion layer according to the invention is applied,
processes can be simplified by omitting side etching, which is an
essential process in a gas phase reaction method. Further, a
process of converting an n-type diffusion layer formed at a back
surface to a p.sup.+-type diffusion layer becomes unnecessary. As a
result, since there is no restriction on the method for forming a
p.sup.+-type diffusion layer at a back surface, the material, the
shape, and the thickness of the back side electrode, it is possible
to select production method, the material and the shape from wide
ranges of choices. In addition, as described below, development of
an internal stress in a semiconductor substrate that is due to the
thickness of a back side electrode can be suppressed, and warpage
of the semiconductor substrate can be suppressed. Further, in the
production of a photovoltaic cell element having a selective
emitter structure or the like, in which an n-type diffusion layer
is formed in a shape of a fine line, the n-type diffusion layer can
be formed only at a position beneath an electrode with high
accuracy. Therefore, it is possible to simplify the production
process by omitting formation of a mask on a semiconductor
substrate for preventing formation of an unnecessary n-type
diffusion layer.
[0017] (Compound Containing Donor Element)
[0018] The composition for forming an n-type diffusion layer
according to the invention includes a compound containing a donor
element. A donor element refers to an element that is capable of
diffusing into a semiconductor substrate to form an n-type
diffusion layer. As a donor element, an element that belongs to
group 15 can be used. From a viewpoint of safety and the like, P
(phosphorus) is preferred.
[0019] There is no particular restriction on a compound containing
a donor element. For example, a metal oxide containing a donor
element can be used. Examples of a metal oxide containing a donor
element include a single metal oxide, such as P.sub.2O.sub.5 and
P.sub.2O.sub.3; an inorganic phosphorus compound, such as
phosphorus silicide, silicon particles doped with phosphorus,
calcium phosphate, phosphoric acid, and glass particles containing
phosphorus; and an organic phosphorus compound, such as phosphonic
acid, phosphonous acid, phosphinic acid, phosphinous acid,
phosphine, phosphine oxide, a phosphate ester, and a phosphite
ester.
[0020] Among these, the donor element is preferably one or more
selected from the group consisting of P.sub.2O.sub.3,
P.sub.2O.sub.5, and a compound that can convert into a compound
containing P.sub.2O.sub.5 at a temperature of a thermal treatment
for diffusing a donor element to a semiconductor substrate (for
example, 800 C or higher) such as ammonium dihydrogen phosphate,
phosphoric acid, phosphonous acid, phosphinic acid, phosphinous
acid, phosphine, phosphine oxide, a phosphate ester and a phosphite
ester. Among these, a compound having a melting point of 1000 C or
less is more preferable. This is because a compound containing a
donor element readily becomes molten while performing thermal
diffusion into a semiconductor substrate, which facilitates uniform
diffusion of the donor element into a semiconductor substrate.
Specifically, as such a compound, at least one selected from the
group consisting of P.sub.2O.sub.5 and glass particles containing
phosphorus is preferred. In a case in which the melting point of a
compound containing a donor element exceeds 1000 C, it is possible
to add a compound having a melting point of below 1000 C such that
the donor element is allowed to diffuse into a semiconductor
substrate via the compound having a melting point of below 1000 C
from the compound containing the donor element.
[0021] The compound containing a donor element may be in a state in
which particles of the composition for forming an n-type diffusion
layer is dispersed in a dispersion medium, or in a state in which
the compound containing a donor element is dissolved in a
dispersion medium. In a case in which the compound containing a
donor element is in the form of solid particles, examples of the
shape thereof include nearly spherical, flat, blockish, platy, and
squamous. From the viewpoint of application suitability of the
composition for forming an n-type diffusion layer onto a substrate
or uniform diffusibility, the shape of the particle is preferably
nearly spherical, flat or platy. In a case in which a compound
containing a donor element is in the shape of solid particles, the
particle size is preferably 100 .mu.m or less. In a case in which
particles having a particle size of 100 .mu.m or less are applied
onto a semiconductor substrate, a flat and smooth layer of a
composition for forming an n-type diffusion layer tends to be
readily formed. Further, when a compound containing a donor element
is in the shape of solid particles, the particle size is more
preferably 50 .mu.m or less. Although there is no particular
restriction on the lower limit, it is preferably 0.01 .mu.m or
more, more preferably 0.1 .mu.m or more. When the compound
containing a donor element is in the form of solid particles, the
particle size of a particle refers to a volume average particle
diameter, which can be measured by a laser scattering diffraction
particle size distribution analyzer and the like. The volume
average particle diameter can be measured by detecting a
relationship between a scattered light intensity and an angle of a
laser beam by which a particle is irradiated, and calculating based
on the Mie scattering theory. Although there is no particular
restriction on a dispersion medium to be used for the measurement,
a dispersion medium in which particles to be measured are not
dissolved is preferred. Further, in a case of particles that do not
form a secondary aggregation, it is also possible to calculate by
measuring the average particle diameter with a scanning electron
microscope.
[0022] In a case of a composition for forming an n-type diffusion
layer in which the compound containing a donor element is dissolved
in a dispersion medium, there is no particular restriction on the
shape of a compound containing a donor element that is to be used
for preparation of the composition for forming an n-type diffusion
layer.
[0023] The content of the compound containing a donor element in
the composition for forming an n-type diffusion layer is determined
in view of application suitability of the composition for forming
an n-type diffusion layer, diffusibility of a donor element, and
the like. In general, the content of the compound containing a
donor element in the composition for forming an n-type diffusion
layer is preferably from 0.1 mass % to 95 mass %, more preferably
from 1 mass % to 90 mass %, further preferably from 1 mass % to 80
mass %, still further preferably from 2 mass % to 80 mass %, and
especially preferably from 5 mass % to 20 mass %, in the
composition for forming an n-type diffusion layer. When the content
of the compound containing a donor element is 0.1 mass % or more,
an n-type diffusion layer can be formed sufficiently. When the
content of the compound containing a donor element is 95 mass % or
less, dispersibility of the compound containing a donor element in
a composition for forming an n-type diffusion layer becomes
favorable, and application suitability with respect to a
semiconductor substrate is improved.
[0024] The compound containing a donor element is preferably glass
particles containing a donor element. The glass refers to a
substance in which a clear crystalline state is not recognized in
its atomic order in an X-ray diffraction spectrum, and has an
irregular network structure and exhibits a glass transition
phenomenon. By using glass particles containing a donor element,
diffusion of a donor element out from a region at which the
composition for forming an n-type diffusion layer has been applied
(also referred to as "out-diffusion") tends to be suppressed more
effectively, and formation of an unnecessary n-type diffusion layer
at a back side and side surfaces can be suppressed. In other words,
by using glass particles containing a donor element, an n-type
diffusion layer can be formed in a more selective manner.
[0025] The glass particles containing a donor element will be
described in detail. In the present invention, the glass particles
contained in the composition for forming an n-type diffusion layer
melt at a temperature during thermal diffusion (approximately from
800 C to 2000 C) and form a glass layer over an n-type diffusion
layer. As a result, the out-diffusion can be further suppressed.
After formation of the n-type diffusion layer, the glass layer
formed on the n-type diffusion layer can be removed by performing
etching (for example, with a hydrofluoric acid aqueous
solution).
[0026] The glass particles containing a donor element can be formed
by, for example, including a substance containing a donor element
and a glass component substance. As a substance containing a donor
element used for introducing a donor element into glass particles,
a compound containing P (phosphorus) is preferable, and at least
one selected from the group consisting of P.sub.2O.sub.3 and
P.sub.2O.sub.5 is more preferable.
[0027] There is no particular restriction on the content of a
substance containing a donor element in the glass particles
containing a donor element. For example, from a viewpoint of
diffusibility of a donor element, the content of the substance
containing a donor element is preferably from 0.5 mass % to 100
mass %, more preferably from 2 mass % to 80 mass %. Further, from a
viewpoint of diffusibility of a donor element, the glass particles
containing a donor element preferably contains, as a substance
containing a donor element, at least one selected from the group
consisting of P.sub.2O.sub.3 and P.sub.2O.sub.5 in an amount from
0.01 mass % to 100 mass %, more preferably from 0.01 mass % to 10
mass %, further preferably from 2 mass % to 10 mass %.
[0028] As necessary, the melting temperature, softening
temperature, glass transition temperature, chemical resistance, and
the like of the glass particles containing a donor element can be
regulated by adjusting the content ratio of the components.
Further, the glass particles containing a donor element preferably
include at least one of the following glass component
substances.
[0029] Examples of the glass component substance include SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, WO.sub.3, MoO.sub.3, MnO,
La.sub.2O.sub.3, Nb.sub.2O.sub.5, Ta.sub.2O.sub.5, Y.sub.2O.sub.3,
CsO.sub.2, TiO.sub.2, ZrO.sub.2, GeO.sub.2, TeO.sub.2, and
Lu.sub.2O.sub.3. Among these, at least one selected from the group
consisting of SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO,
CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2,
MoO.sub.3, GeO.sub.2, Y.sub.2O.sub.3, CsO.sub.2 and TiO.sub.2 is
preferably used, and at least one selected from the group
consisting of SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO,
CaO, MgO, BeO, ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and
MoO.sub.3 is more preferably used.
[0030] Specific examples of the glass particles containing a donor
element include a system containing both the substance containing a
donor element and the glass component substance. More specifically,
the examples include glass particles of systems containing
P.sub.2O.sub.5 as a substance containing a donor element, such as a
P.sub.2O.sub.5--SiO.sub.2 system (described in the order of
substance containing a donor element-glass component substance,
hereinafter the same shall apply), a P.sub.2O.sub.5--K.sub.2O
system, a P.sub.2O.sub.5--Na.sub.2O system, a
P.sub.2O.sub.5--Li.sub.2O system, a P.sub.2O.sub.5--BaO system, a
P.sub.2O.sub.5--SrO system, a P.sub.2O.sub.5--CaO system, a
P.sub.2O.sub.5--MgO system, a P.sub.2O.sub.5--BeO system, a
P.sub.2O.sub.5--ZnO system, a P.sub.2O.sub.5--CdO system, a
P.sub.2O.sub.5--PbO system, a P.sub.2O.sub.5--V.sub.2O.sub.5
system, a P.sub.2O.sub.5--SnO system, a P.sub.2O.sub.5--GeO.sub.2
system, and a P.sub.2O.sub.5--TeO.sub.2 system, and glass particles
of these systems containing P.sub.2O.sub.3 instead of
P.sub.2O.sub.5. The glass particles may contain two or more kinds
of substances containing a donor element, such as a
P.sub.2O.sub.5--Sb.sub.2O.sub.3 system and a
P.sub.2O.sub.5--As.sub.2O.sub.3 system.
[0031] Although examples of a composite glass including two
components are listed above, glass particles including a substance
with three or more components, such as
P.sub.2O.sub.5--SiO.sub.2--V.sub.2O.sub.5 and
P.sub.2O.sub.5--SiO.sub.2--CaO, may be used.
[0032] Preferably, the glass particles include at least one
substance containing a donor element selected from the group
consisting of P.sub.2O.sub.3 and P.sub.2O.sub.5, and at least one
glass component substance selected from the group consisting of
SiO.sub.2, K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO,
ZnO, PbO, CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2, MoO.sub.3,
GeO.sub.2, Y.sub.2O.sub.3, CsO.sub.2 and TiO.sub.2. More
preferably, the glass particles include at least one substance
containing a donor element selected from the group consisting of
P.sub.2O.sub.3 and P.sub.2O.sub.5, and at least one glass component
substance selected from the group consisting of SiO.sub.2,
K.sub.2O, Na.sub.2O, Li.sub.2O, BaO, SrO, CaO, MgO, BeO, ZnO, PbO,
CdO, V.sub.2O.sub.5, SnO, ZrO.sub.2 and MoO.sub.3. Further
preferably, the glass particles include P.sub.2O.sub.5 as a
substance containing a donor element, and at least one glass
component substance selected from the group consisting of
SiO.sub.2, ZnO, CaO, Na.sub.2O, Li.sub.2O and BaO. Use of glass
particles as mentioned above enables a further lowering in a sheet
resistance of a n-type diffusion layer to be formed.
[0033] The content of the glass component substance selected from
the group consisting of SiO.sub.2 and GeO.sub.2 (hereinafter, also
referred to as a "specific glass component substance") in the glass
particles is preferably determined in view of the melting
temperature, softening point, glass transition point, and chemical
resistance. In general, the content of a specific glass component
substance in 100 mass % of the glass particles is preferably from
0.01 mass % to 80 mass %, more preferably from 0.1 mass % to 50
mass %. When the content of the specific glass component substance
is 0.01 mass % or more, an n-type diffusion layer can be
efficiently formed. When the content of the specific glass
component substance is 80 mass % or less, formation of an n-type
diffusion layer at a region to which a composition for forming an
n-type diffusion layer has not been applied can be effectively
suppressed.
[0034] The glass particles may include a network modifying oxide
(for example, an alkali oxide or an alkaline-earth oxide) or an
intermediate oxide that does not vitrify alone, in addition to the
specific glass component substance. Specifically, in a case of
P.sub.2O.sub.5--SiO.sub.2--CaO glass, the content of CaO as a
network modifying oxide is preferably from 1 mass % to 30 mass %,
more preferably from 5 mass % to 20 mass %.
[0035] The softening point of the glass particles is preferably
from 200 C to 1000 C from viewpoints of diffusibility and dripping
during a thermal treatment, more preferably from 300 C to 900 C.
The softening point of the glass particles can be determined from a
differential thermal analysis (DTA) curve obtained with a
simultaneous thermogravimetry/differential thermal analysis
apparatus. Specifically, a third peak from the low temperature side
of a DTA curve can be defined as a softening point.
[0036] The glass particles including a donor element can be
produced according to the following procedures.
[0037] First, the source materials, for example, a substance
containing a donor element and a glass component substance are
weighed and placed in a crucible. Examples of the material of the
crucible include platinum, platinum-rhodium, iridium, alumina,
quartz and carbon, which is selected appropriately in view of the
melting temperature, atmosphere, reactivity with a molten
substance, and the like. Next, the source materials are heated at a
temperature that is determined according to the glass composition
in an electrical oven, thereby obtaining a melt. During heating,
the source materials are preferably stirred such that a uniform
melt is obtained. Then, the obtained melt is cast over a zirconia
substrate, a carbon substrate, or the like, and vitrified. Finally,
the glass is pulverized into a powder. The pulverization may be
performed by a known method, such as jet milling, bead milling, and
ball milling.
[0038] (Dispersion Medium)
[0039] The composition for forming an n-type diffusion layer
according to the invention includes a dispersion medium.
[0040] A dispersion medium refers to a medium that disperses or
dissolves the compound containing a donor element and the organic
filler in a composition. Specifically, the dispersion medium
preferably includes at least a solvent or water. The dispersion
medium may include an organic binder as described below, in
addition to the solvent or water.
[0041] Examples of a solvent include a ketone solvent, such as
acetone, methyl ethyl ketone, methyl n-propyl ketone, methyl
isopropyl ketone, methyl n-butyl ketone, methyl isobutyl ketone,
methyl n-pentyl ketone, methyl n-hexyl ketone, diethyl ketone,
dipropyl ketone, diisobutyl ketone, trimethylnonanone,
cyclohexanone, cyclopentanone, methylcyclohexanone,
2,4-pentanedione, and acetonylacetone; an ether solvent, such as
diethyl ether, methyl ethyl ether, methyl n-propyl ether,
diisopropyl ether, tetrahydrofuran, methyltetrahydrofuran, dioxane,
dimethyldioxane, ethylene glycol dimethyl ether, ethylene glycol
diethyl ether, ethylene glycol di n-propyl ether, ethylene glycol
dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol
diethyl ether, diethylene glycol methyl ethyl ether, diethylene
glycol methyl-n-propyl ether, diethylene glycol methyl n-butyl
ether, diethylene glycol di-n-propyl ether, diethylene glycol
di-n-butyl ether, diethylene glycol methyl n-hexylether,
triethylene glycol dimethyl ether, triethylene glycol diethyl
ether, triethylene glycol methyl ethyl ether, triethylene glycol
methyl-n-butyl ether, triethylene glycol di-n-butyl ether,
triethylene glycol methyl-n-hexyl ether, tetraethylene glycol
dimethyl ether, tetraethylene glycol diethyl ether, tetraethylene
glycol methyl ethyl ether, tetraethylene glycol methyl-n-butyl
ether, tetraethylene glycol di-n-butyl ether, tetraethylene glycol
methyl n-hexyl ether, tetraethylene glycol di-n-butyl ether,
propylene glycol dimethyl ether, propylene glycol diethyl ether,
propylene glycol di-n-propyl ether, propylene glycol dibutyl ether,
dipropylene glycol dimethyl ether, dipropylene glycol diethyl
ether, dipropylene glycol methyl ethyl ether, dipropylene glycol
methyl-n-butyl ether, dipropylene glycol di-n-propyl ether,
dipropylene glycol di-n-butyl ether, dipropylene glycol
methyl-n-hexylether, tripropylene glycol dimethyl ether,
tripropylene glycol diethyl ether, tripropylene glycol methyl ethyl
ether, tripropylene glycol methyl-n-butyl ether, tripropylene
glycol di-n-butyl ether, tripropylene glycol methyl-n-hexyl ether,
tetrapropylene glycol dimethyl ether, tetrapropylene glycol diethyl
ether, tetradipropylene glycol methyl ethyl ether, tetrapropylene
glycol methyl n-butyl ether, tetrapropylene glycol di-n-butyl
ether, tetrapropylene glycol methyl n-hexyl ether, and
tetrapropylene glycol di-n-butyl ether; an ester solvent, such as
methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate,
n-butyl acetate, isobutyl acetate, 2-butyl acetate, n-pentyl
acetate, sec-pentyl acetate, 3-methoxybutyl acetate, methylpentyl
acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate,
2-(2-butoxyethoxy)ethyl acetate, benzyl acetate, cyclohexyl
acetate, methylcyclohexyl acetate, nonyl acetate, methyl
acetoacetate, ethyl acetoacetate, diethylene glycol methyl ether
acetate, diethylene glycol monoethyl ether acetate, dipropylene
glycol methyl ether acetate, dipropylene glycol ethyl ether
acetate, glycol diacetate, methoxytriglycol acetate, ethyl
propionate, n-butyl propionate, isoamyl propionate, diethyl
oxalate, di-n-butyl oxalate, methyl lactate, ethyl lactate, n-butyl
lactate, n-amyl lactate, ethylene glycol methyl ether propionate,
ethylene glycol ethyl ether propionate, ethylene glycol methyl
ether acetate, ethylene glycol ethyl ether acetate, propylene
glycol methyl ether acetate, propylene glycol ethyl ether acetate,
propylene glycol propyl ether acetate, .gamma.-butyrolactone, and
.gamma.-valerolactone; an aprotic polar solvent, such as
acetonitrile, N-methylpyrrolidinone, N-ethylpyrrolidinone,
N-propylpyrrolidinone, N-butylpyrrolidinone, N-hexylpyrrolidinone,
N-cyclohexylpyrrolidinone, N,N-dimethylformamide,
N,N-dimethylacetamide, and dimethyl sulfoxide; an alcohol solvent,
such as methanol, ethanol, n-propanol, isopropanol, n-butanol,
isobutanol, 2-butanol, t-butanol, n-pentanol, isopentanol,
2-methylbutanol, 2-pentanol, t-pentanol, 3-methoxybutanol,
n-hexanol, 2-methylpentanol, 2-hexanol, 2-ethylbutanol, 2-heptanol,
n-octanol, 2-ethylhexanol, 2-octanol, n-nonyl alcohol, n-decanol,
2-undecyl alcohol, trimethylnonyl alcohol, 2-tetradecyl alcohol,
2-heptadecyl alcohol, phenol, cyclohexanol, methylcyclohexanol,
benzyl alcohol, ethylene glycol, 1,2-propylene glycol, 1,3-butylene
glycol, diethylene glycol, dipropylene glycol, triethylene glycol,
tripropylene glycol, and isobornyl cyclohexanol; a glycol monoether
solvent, such as ethylene glycol monomethyl ether, ethylene glycol
monoethyl ether, ethylene glycol monophenyl ether, diethylene
glycol monomethyl ether, diethylene glycol monoethyl ether,
diethylene glycol mono-n-butyl ether, diethylene glycol
mono-n-hexyl ether, ethoxytriglycol, tetraethylene glycol
mono-n-butyl ether, propylene glycol monomethyl ether, dipropylene
glycol monomethyl ether, dipropylene glycol monoethyl ether, and
tripropylene glycol monomethyl ether; a terpene solvent including
terpinene such as .alpha.-terpinene, terpineol such as
.alpha.-terpineol, myrcene, allo-ocimene, limonene, dipentene,
pinene such as .alpha.-pinene and .beta.-pinene, carvone, ocimene,
and phellandrene; and water. The solvent may be used singly or in a
combination of two or more kinds thereof.
[0042] From the viewpoint of application suitability of the
composition for forming an n-type diffusion layer to a
semiconductor substrate, the solvent preferably includes at least
one selected from the group consisting of an ester solvent, a
glycol monoether solvent and a terpene solvent, more preferably at
least one selected from the group consisting of
2-(2-butoxyethoxy)ethyl acetate, diethylene glycol mono-n-butyl
ether, and .alpha.-terpineol.
[0043] The content of the dispersion medium in the composition for
forming an n-type diffusion layer is determined in view of
application suitability and the concentration of a donor element.
For example, the content of the dispersion medium in the
composition for forming an n-type diffusion layer is preferably
from 5 mass % to 99 mass %, more preferably from 20 mass % to 95
mass %, further preferably from 40 mass % to 90 mass %. When the
dispersion medium includes an organic binder, the total amount of
the organic binder and the solvent or water is preferably within
the above range.
[0044] (Organic Filler)
[0045] The composition for forming an n-type diffusion layer
according to the invention includes an organic filler. The organic
filler refers to an organic compound in the form of particles or
fibers. Since the composition for forming an n-type diffusion layer
according to the invention includes an organic filler, it is
possible to apply the composition for forming an n-type diffusion
layer onto a semiconductor substrate into a shape of a fine line
pattern of a desired size. In other words, because of the presence
of an organic filler, expansion of a fine line pattern can be
prevented. This is presumably because the organic filler imparts an
appropriate thixotropy to the composition for forming an n-type
diffusion layer. Further, by including the organic filler, an
n-type diffusion layer can be formed into a desired shape without
inhibiting diffusion of a donor element into a semiconductor
substrate. In a case in which an inorganic filler is used instead
of an organic filler, the filler does not disappear during thermal
diffusion and remains. As a result, a glass layer formed from a
molten glass particles tends to become ununiform and prevent
diffusion of a donor element into a semiconductor substrate tends
to be inhibited.
[0046] Examples of an organic compound that forms an organic filler
include a urea formaldehyde resin, a phenol resin, a polycarbonate
resin, a melamine resin, an epoxy resin, an unsaturated polyester
resin, a silicone resin, a polyurethane resin, a polyolefin resin,
an acrylic resin, a fluorocarbon resin, a polystyrene resin,
cellulose, a formaldehyde resin, a coumarone-indene resin, lignin,
a petroleum resin, an amino resin, a polyester resin, a polyether
sulfone resin, a butadiene resin, and copolymers thereof. The
organic compound may be used singly or in a combination of two or
more kinds thereof.
[0047] Among these, as an organic compound that forms an organic
filler, a compound that degrades at 700 C or less is preferable.
When an organic compound that forms an organic filler degrades at
700 C or less, remaining of the organic filler or its
thermal-treated product without disappearing after formation of an
n-type diffusion layer can be prevented. If the organic filler
remains, it may cause deterioration of the electricity generation
performance of a photovoltaic cell. An organic filler that degrades
at 400 C or less is preferred, and an organic filler that degrades
at 300 C or less is more preferred. Although there is no particular
restriction on the lower limit to the degradation temperature of an
organic filler, it is preferably 150 C or more from a viewpoint of
handleability at the application process, more preferably 200 C or
more. The degradation temperature of an organic filler refers to a
temperature at which the organic filler degrades and disappears,
and can be measured by a thermogravimetric analyzer (DTG-60H, by
Shimadzu Corporation). When the composition for forming an n-type
diffusion layer, in which a dispersion medium that disappears at a
degradation temperature of an organic filler or lower, is heated to
the degradation temperature of an organic filler or higher, the
dispersion medium and the organic filler disappear, whereby only
the compound containing a donor element such as glass particles
remains.
[0048] As an organic compound that forms an organic filler, at
least one selected from the group consisting of an acrylic resin, a
cellulose resin and a polystyrene resin is preferable from a
viewpoint of thermal degradability, and an acrylic resin is more
preferable.
[0049] Examples of a monomer that constitutes the acrylic resin
include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl
acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl
methacrylate, isobutyl acrylate, isobutyl methacrylate, 2-butyl
acrylate, 2-butyl methacrylate, tert-butyl acrylate, tert-butyl
methacrylate, pentyl acrylate, pentyl methacrylate, hexyl acrylate,
hexyl methacrylate, heptyl acrylate, heptyl methacrylate,
2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, octyl acrylate,
octyl methacrylate, nonyl acrylate, nonyl methacrylate, decyl
acrylate, decyl methacrylate, dodecyl acrylate, dodecyl
methacrylate, tetradecyl acrylate, tetradecyl methacrylate,
hexadecyl acrylate, hexadecyl methacrylate, octadecyl acrylate,
octadecyl methacrylate, eicosyl acrylate, eicosyl methacrylate,
dococyl acrylate, dococyl methacrylate, cyclopentyl acrylate,
cyclopentyl methacrylate, cyclohexyl acrylate, cyclohexyl
methacrylate, cycloheptyl acrylate, cycloheptyl methacrylate,
benzyl acrylate, benzyl methacrylate, phenyl acrylate, phenyl
methacrylate, methoxyethyl acrylate, methoxyethyl methacrylate,
dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate,
diethylaminoethyl acrylate, diethylaminoethyl methacrylate,
dimethylaminopropyl acrylate, dimethylaminopropyl methacrylate,
2-chloroethyl acrylate, 2-chloroethyl methacrylate, 2-fluoroethyl
acrylate, 2-fluoroethyl methacrylate, styrene,
.alpha.-methylstyrene, cyclohexylmaleimide, dicyclopentanyl
acrylate, dicyclopentanyl methacrylate, vinyltoluene, vinyl
chloride, vinyl acetate, N-vinylpyrrolidone, butadiene, isoprene,
and chloroprene. The monomers may be used singly or in a
combination of two or more kinds thereof.
[0050] When the organic filler is in the form of particles, the
average particle size is preferably 10 .mu.m or less, more
preferably 1 .mu.m or less, further preferably 0.1 .mu.m or less.
When the average particle size of the organic filler is 10 .mu.m or
less, occurrence of precipitation in the composition for forming an
n-type diffusion layer tends to be suppressed. Further, in a case
in which the composition for forming an n-type diffusion layer is
applied to a semiconductor substrate by a screen printing method, a
factor that causes clogging of meshes of a printing mask can be
removed. The average particle size of the organic filler can be
measured by a particle size distribution analyzer based on a laser
diffraction scattering method (LS13320, by Beckman Coulter, Inc.)
and a median diameter calculated from the obtained particle size
distribution may be defined as the average particle size.
Alternatively, the average particle size may be determined through
observation with a SEM (scanning electron microscope).
[0051] When the organic filler is in the form of fibers, the
organic filler may be used without particular restriction, insofar
as the object of the invention can be achieved.
[0052] There is no particular restriction on the molecular weight
of an organic compound to be used as the organic filler, and is
preferably adjusted appropriately in view of a desired viscosity of
the composition for forming an n-type diffusion layer. The content
of the organic filler in the composition for forming an n-type
diffusion layer is preferably from 1 mass % to 50 mass %.
[0053] In the composition for forming an n-type diffusion layer,
the mass ratio of the compound containing a donor element to the
organic filler (compound containing a donor element:organic filler)
is preferably from 1:50 to 50:1, more preferably from 1:10 to 10:1,
further preferably from 1:5 to 5:1.
[0054] As necessary, the composition for forming an n-type
diffusion layer according to the invention may include an organic
binder, a surfactant, an inorganic powder, a resin containing a
silicon atom, a deducing compound and the like, in addition to the
compound containing a donor element, the organic filler, and the
dispersion medium.
[0055] The composition for forming an n-type diffusion layer
preferably further includes at least one organic binder. By
including an organic binder, the viscosity of the composition for
forming an n-type diffusion layer can be adjusted or thixotropy can
be imparted, whereby the application suitability with respect to a
semiconductor substrate can be improved. The organic binder can be
selected appropriately from polyvinyl alcohol; a polyacrylamide
resin; a polyvinylamide resin; a polyvinylpyrrolidone resin; a
poly(ethylene oxide) resin; a polysulfone resin; an acrylamide
alkylsulfonic acid resin; a cellulose derivative, such as cellulose
ether, carboxy methyl cellulose, hydroxy ethyl cellulose, and ethyl
cellulose; gelatin and a gelatin derivative; starch and a starch
derivative; sodium alginate and a sodium alginate derivative;
xanthan and a xanthan derivative; guar and a guar derivative;
scleroglucan and a scleroglucan derivative; tragacanth and a
tragacanth derivative; dextrin and a dextrin derivative; a
(meth)acrylic acid resin; a (meth)acrylate resin, such as an alkyl
(meth)acrylate resin, and a dimethylaminoethyl (meth)acrylate
resin; a butadiene resin; a styrenic resin; and copolymers thereof.
The organic binder may be used singly or in a combination of two or
more kinds thereof. When the organic binder is used, at least one
selected from the group consisting of a cellulose derivative, an
acrylic resin derivative, and a poly(ethylene oxide) resin is
preferred in view of degradability and handleability.
[0056] The molecular weight of the organic binder is not
particularly restricted, and is preferably adjusted appropriately
in view of a desired viscosity of the composition for forming an
n-type diffusion layer. Further, when the composition for forming
an n-type diffusion layer includes an organic binder, the content
thereof in the composition for forming an n-type diffusion layer is
preferably from 0.5 mass % to 30 mass %, more preferably from 3
mass % to 25 mass %, further preferably from 3 mass % to 20 mass
%.
[0057] Examples of a surfactant include a nonionic surfactant, a
cationic surfactant, and an anionic surfactant. Among them, a
nonionic surfactant or a cationic surfactant is preferable and a
nonionic surfactant is more preferable, because the amount of
impurity such as a heavy metal that may be introduced is smaller.
Examples of the nonionic surfactant include a silicon surfactant, a
fluorine surfactant, and a hydrocarbon surfactant. Among these, a
hydrocarbon surfactant, which disappears rapidly during heating for
diffusion or the like, is preferred.
[0058] Examples of the hydrocarbon surfactant include a block
copolymer of ethylene oxide and propylene oxide, and an acetylene
glycol compound. From a viewpoint of more suppressing variation in
the sheet resistance of a semiconductor substrate, an acetylene
glycol compound is preferable.
[0059] As an inorganic powder, a substance that can function as a
filler is preferable. Examples of an inorganic powder include
silicon oxide, titanium oxide, silicon nitride, and silicon
carbide.
[0060] Examples of a resin containing a silicon atom include a
silicone resin.
[0061] Examples of a reducing compound include a polyalkylene
glycol such as polyethylene glycol and polypropylene glycol, and a
terminally alkylated polyalkylene glycol; a monosaccharide such as
glucose, fructose and galactose, and a derivative of a
monosaccharide; a disaccharide such as sucrose and maltose, and a
derivative of a disaccharide; and a polysaccharide and a derivative
of a polysaccharide. Among the reducing compounds, a polyalkylene
glycol is preferable, and polypropylene glycol is further
preferable. Addition of a reducing compound to the composition for
forming an n-type diffusion layer may facilitate diffusion of a
donor element into a semiconductor substrate.
[0062] There is no particular restriction on the method for
producing the composition for forming an n-type diffusion layer.
For example, the composition can be produced by mixing a compound
containing a donor element, an organic filler, an dispersion
medium, and other components if necessary, with a blender, a mixer,
a mortar or a rotor. The mixing may be performed while heating, as
desired. In a case of heating during mixing, the temperature may be
between 30 C and 100 C, for example.
[0063] The components in the composition for forming an n-type
diffusion layer and the content of the components can be identified
by way of thermal analysis such as TG/DTA, NMR, HPLC, GEL
permeation chromatography, GC-MS, IR, MALDI-MS and the like.
[0064] The viscoelasticity as a shear viscosity at 25 C at a shear
rate of 0.01/sec of the composition for forming an n-type diffusion
layer is preferably from 50 Pas to 10000 Pas, more preferably from
300 Pas to 7000 Pas, further preferably from 1000 Pas to 5000 Pas,
in view of application suitability of the composition for forming
an n-type diffusion layer.
[0065] A thixotropic characteristic of the composition for forming
an n-type diffusion layer (hereinafter, referred to as
"thixotropy") can be represented by a TI value, which is defined as
[log.sub.10(.eta..sup.0.01)-log.sub.10(.eta..sup.10)], wherein the
logarithm of a shear viscosity .eta..sup.x at 25 C and at a shear
rate of x[s.sup.-1] is expressed as log.sub.10(.eta..sub.x). The TI
value is preferably from 0.5 to 6.0, more preferably from 0.5 to
4.0, further preferably from 0.5 to 3.0. The shear viscosity can be
measured with a viscoelasticity measuring apparatus (Rheometer
MCR301, made by Anton Paar GmbH).
[0066] <Method for Producing Semiconductor Substrate Having
n-Type Diffusion Layer>
[0067] The method for producing a semiconductor substrate having an
n-type diffusion layer according to the invention includes a
process of applying the composition for forming an n-type diffusion
layer according to the invention onto at least a part of a
semiconductor substrate; and a process of forming an n-type
diffusion layer in the semiconductor substrate by performing a heat
treatment.
[0068] There is no particular restriction on the method for
applying a composition for forming an n-type diffusion layer
according to the invention onto a semiconductor substrate, and the
method may be selected from a printing method, a spin coating
method, a brushing method, a spraying method, a doctor blade
method, a roll coater method, an ink jet method, and the like, in
view of the application.
[0069] In the method of producing a semiconductor substrate having
an n-type diffusion layer according to the invention, there is no
particular restriction on the method for performing a thermal
treatment to the composition for forming an n-type diffusion layer
that has been applied onto a semiconductor substrate. For example,
the thermal treatment temperature may be between 600 C and 1200 C,
and the thermal treatment time may be between 1 minute and 60
minutes. There is no particular restriction on an apparatus for
performing the thermal treatment, and it may be a known continuous
furnace, a batch furnace, or the like.
[0070] <Method for Producing Photovoltaic Cell Element>
[0071] The method for producing a photovoltaic cell element
according to the invention includes a process of applying the
composition for forming an n-type diffusion layer according to the
invention onto at least a part of a semiconductor substrate; a
process of forming an n-type diffusion layer in the semiconductor
substrate by performing a thermal treatment; and a process of
forming an electrode on the n-type diffusion layer.
[0072] Examples of a method for forming an electrode on an n-type
diffusion layer include a method in which a metal paste for forming
an electrode that contains an electrode material is applied onto a
desired region of a semiconductor substrate, dried as necessary,
and then thermally treated; a method in which plating is performed
with an electrode material to form an electrode; and a method in
which an electrode material is deposited in a high vacuum by
electron beam heating to form an electrode. Examples of a method
for applying a metal paste for forming an electrode to a
semiconductor substrate include a printing method, a spin coating
method, a brushing method, a spraying method, a doctor blade
method, a roll coater method, and an ink jet method. There is no
particular restriction on the composition of a metal paste for an
electrode. For example, the metal paste may include metal particles
and glass particles as essential components, and if necessary, a
resin binder or other additives.
[0073] Next, the method for producing a semiconductor substrate
having an n-type diffusion layer and a photovoltaic cell element
according to the invention will be described by referring to the
drawings. FIG. 1 is a conceptual schematic cross-sectional view
showing an example of processes for producing a photovoltaic cell
element having a selective emitter structure according to the
present embodiment. In the drawings, the same components are
indicated by the same reference number.
[0074] First, a p-type semiconductor substrate 10 shown in FIG. 1
(1) is prepared. The p-type semiconductor substrate 10 is provided
with a textured structure at a surface that serves as a light
receiving surface when assembled to a photovoltaic cell element.
More specifically, a damaged layer on a surface of a p-type
semiconductor substrate 10, which is formed upon slicing off from
an ingot, is removed with 20 mass % caustic soda. Next, etching is
performed with a mixture liquid of 1 mass % caustic soda and 10
mass % isopropyl alcohol, thereby forming a textured structure (not
shown in the drawing). By forming a textured structure at a light
receiving surface (top surface), a light trapping effect is
promoted and a high efficiency is achieved.
[0075] Next, as shown in FIG. 1 (2), on the top surface of the
p-type semiconductor substrate 10, i.e., a surface that serves as a
light receiving surface of a photovoltaic cell element, a
composition for forming an n-type diffusion layer 11 is applied
into a shape of fine line. There is no particular restriction on
the method for applying the composition for forming an n-type
diffusion layer 11 according to the invention, and examples of the
method include a printing method, a spin coating method, a brushing
method, a spraying method, a doctor blade method, a roll coater
method, and an ink jet method. The application amount of the
composition for forming an n-type diffusion layer 11 is preferably
from 0.01 g/m.sup.2 to 100 g/m.sup.2, more preferably from 0.1
g/m.sup.2 to 10 g/m.sup.2.
[0076] Expansion of the line width of a fine line formed by
applying the composition for forming an n-type diffusion layer 11
is preferably within 100 .mu.m from a predetermined value, more
preferably within 35 .mu.m, further preferably within 10 .mu.m, and
still further preferably within 5 .mu.m.
[0077] For example, when the composition for forming an n-type
diffusion layer 11 is applied onto a semiconductor substrate into a
line having a width of 150 .mu.m, the width of the composition for
forming an n-type diffusion layer 11 as measured after drying is
preferably 250 .mu.m or less, more preferably 185 .mu.m or less,
further preferably 160 .mu.m or less, still further preferably 155
.mu.m or less.
[0078] The expansion rate of the line width of a fine line formed
by applying the composition for forming an n-type diffusion layer
11 is preferably within 67% of a predetermined value, more
preferably within 25%, further preferably within 5%.
[0079] In a case in which the composition for forming an n-type
diffusion layer includes a solvent, a drying process may be
necessary in order to evaporate the solvent in the composition for
forming an n-type diffusion layer that has been applied onto a
semiconductor substrate. For example, the drying is performed at a
temperature of approximately from 80 C to 300 C, for a time of from
1 minute to 10 minutes with a hot plate or from 10 minutes to 30
minutes with a drier. The drying conditions depend on the
composition of a solvent contained in the applied composition for
forming an n-type diffusion layer, and are not particularly
restricted to the above conditions according to the invention.
[0080] Next, as shown in FIG. 1 (3), the semiconductor substrate
10, to which the composition for forming an n-type diffusion layer
11 has been applied, is subjected to a thermal treatment. Although
there is no particular restriction on the thermal treatment
temperature, it is preferably from 600 C to 1200 C, more preferably
from 750 C to 1050 C. Although there is no particular restriction
on the thermal diffusion treatment time, it is preferably between 1
minute and 30 minutes. By performing the thermal treatment, a donor
element diffuses into the semiconductor substrate and an n-type
diffusion layer 12 is formed. The thermal treatment may be
performed with a known device such as a continuous furnace, a
batch-wise furnace or the like. Since a glass layer (not
illustrated) such as phosphate glass is formed on a surface of the
n-type diffusion layer 12, it is removed by performing etching. The
etching may be performed by a known method such as a method of
immersing in an acid like hydrofluoric acid or a method of
immersing in an alkali like caustic soda.
[0081] Further, as shown in FIG. 1 (4), at a region of the light
receiving surface other than a portion at which the composition for
forming an n-type diffusion layer 11 has been applied, an n-type
diffusion layer 13 having a lower phosphorus concentration than the
n-type diffusion layer 12 is formed. There is no particular
restriction on a method of forming an n-type diffusion layer 13,
and may be a gas phase reaction method in which a composition for
forming an n-type diffusion layer having a lower content of a
phosphorus compound, or phosphorus oxychloride is used, for
example.
[0082] As shown in FIGS. 1 (2) and (3), according to the method of
the invention in which an n-type diffusion layer 12 is formed with
a composition for forming an n-type diffusion layer 11, an n-type
diffusion layer 12 is formed only at a desired region of a
semiconductor substrate, while not forming an unnecessary n-type
diffusion layer at the back side or side surfaces. Consequently,
the process can be simplified by omitting a side etching process
for removing an unnecessary n-type diffusion layer, which has been
an essential process in a method of forming an n-type diffusion
layer by a conventional gas phase reaction method. Nevertheless,
when an n-type diffusion layer 13 is formed by a gas phase reaction
method, a side etching process needs to be performed.
[0083] As shown in FIG. 1 (5), an antireflection film 14 may be
formed on the n-type diffusion layer 12. An antireflection film 14
can be formed by a known technique. For example, in a case of
forming a silicon nitride film as an antireflection film 14, the
film may be formed by a plasma CVD method using a mixed gas of
SiH.sub.4 and NH.sub.3 as a source material. In that case, hydrogen
diffuses into a crystal and bonds with an orbit that does not
contribute to a bond with a silicon atom, i.e., a dangling bond,
whereby a defect is inactivated (hydrogen passivation). More
specifically, the film is formed under the conditions of a flow
rate ratio of a mixed gas NH.sub.3/SiH.sub.4 of from 0.05 to 1.0,
the pressure in a reactor of from 13.3 Pa to 266.6 Pa (0.1 Torr to
2 Torr), the temperature at film formation of from 300 C to 550 C,
and the frequency for plasma discharge of 100 kHz or more. Although
there is no particular restriction on the film thickness of the
antireflection film, it is preferably from 10 nm to 300 nm, more
preferably from 30 nm to 150 nm.
[0084] Then, as shown in FIG. 1 (6), a metal paste for a top
surface electrode is applied by a screen printing method onto the
antireflection film 14 formed at the top surface (light receiving
surface) of a p-type semiconductor substrate, and dried to form a
top surface electrode 15. Although there is no particular
restriction on the composition of a metal paste for a top surface
electrode, it may include metal particles and glass particles as
essential components, and a resin binder or other additives as
necessary.
[0085] Then, a p.sup.+-type diffusion layer (high concentration
electric field layer) 16 and a back side electrode 17 are formed at
the back side of the p-type semiconductor substrate 10. Generally,
a layer of a metal paste for a back side electrode containing
aluminum is formed at a back side electrode of the p-type
semiconductor substrate 10, and the layer is sintered to form a
back side electrode 17 and a p.sup.+-type diffusion layer 16 by
diffusing aluminum into the back side of the p-type semiconductor
substrate 10, at the same time. At this time, a silver paste for
forming a silver electrode may be applied at a portion of the back
side for forming a connection between devices at a module process
step.
[0086] In a conventional production method, it is necessary to
convert an n-type diffusion layer, which is formed by diffusion of
phosphorus at the back side of a semiconductor substrate, to a
p-type diffusion layer by using aluminum or the like. In this
method, in order to achieve a sufficient conversion into a p-type
diffusion layer and also forming a p.sup.+-type diffusion layer, a
thick aluminum layer needs to be formed in order to secure a
sufficient amount of aluminum. However, since the coefficient of
thermal expansion of aluminum is significantly different from the
coefficient of thermal expansion of silicon used as the substrate,
a large internal stress is developed in the semiconductor substrate
during the process of firing and cooling, which may cause warpage
of the semiconductor substrate.
[0087] Therefore, there is a problem in that the internal stress
may damage crystal grain boundaries of crystals, resulting in a
large electric power loss. Further, warpage of a semiconductor
substrate tends to cause breakage of a photovoltaic cell element
during conveyance of a photovoltaic cell element or connecting the
same with a copper line, referred to as a tab line, in a module
process. Further, due to a recent improvement in slicing
techniques, the thickness of a semiconductor substrate has been
reducing and a photovoltaic cell element is becoming easier to
crack.
[0088] In the production method according to the invention, since
an unnecessary n-type diffusion layer is not formed on the back
side of a semiconductor substrate, converting an n-type diffusion
layer to a p-type diffusion layer need not be performed and an
aluminum layer needs not to be thickened. As a result, development
of an internal stress in a semiconductor substrate or warpage of a
semiconductor substrate can be suppressed. Consequently, an
increase in electric power loss or breakage of a photovoltaic cell
element can be suppressed.
[0089] In the production method according to the invention, the
method for forming a p.sup.+-type diffusion layer 16 at the back
side is not limited to a method of using a metal paste for a back
side electrode containing aluminum, and any conventional method may
be employed from a wide range of choices. For example, a
p.sup.+-type diffusion layer 16 can be formed by applying a
composition for forming a p-type diffusion layer containing a group
13 element, such as boron, onto the back side of a semiconductor
substrate.
[0090] In the production method according to the invention, the
material for a back side electrode 17 is not limited to aluminum
that belongs to group 13, and may be silver, copper or the like. It
is also possible to reduce the thickness of a back side electrode
17 than a conventional electrode. There is no particular
restriction on a material or a formation method for a back side
electrode 17. For example, a back side electrode 17 may be formed
by applying a paste for a back side electrode containing a metal
such as aluminum, silver or copper onto the back side of a
semiconductor substrate, and drying the same. In that case, a
silver paste for forming a silver electrode may be applied also at
a portion of the back side of a semiconductor substrate for forming
a connection between photovoltaic cell elements in a module
process.
[0091] In FIG. 1 (7), the electrodes are sintered and a
photovoltaic cell element is obtained. The temperature for the
sintering may be, for example, in a range of from 600 C to 900 C,
and the time may be, for example, several seconds to several
minutes. In that case, at the top surface side of a semiconductor
substrate, the antireflection film 14 provided as an insulation
film is molten by means of glass particles in the metal paste for
an electrode, and a part of the surface of a p-type semiconductor
substrate 10 is also molten, whereby a contact is formed between
metal particles (for example, silver particles) in the metal paste
for an electrode solidifies and the semiconductor substrate 10. As
a result, conduction between the top surface electrodes 15 and the
semiconductor substrate 10, which is referred to as fire-through,
is established.
[0092] Examples of the configuration of a top surface electrode 15
include a configuration in which bus bar electrodes 30 are
positioned across finger electrodes 32, as shown in FIG. 2 and FIG.
3. FIG. 2 is a plan view of a photovoltaic cell element having top
surface electrodes 15 formed of bus bar electrodes 30 and finger
electrodes 32 intersecting with each other as viewed from the top
surface. FIG. 3 is an enlarged perspective view of a part of FIG.
2, in which top surface electrodes 15 penetrate an antireflection
layer 20 on the semiconductor substrate 10.
[0093] The top surface electrode 15 having a structure as mentioned
above can be formed by, for example, applying a metal paste for an
electrode by screen printing or the like, and performing a
sintering treatment as described above. Alternatively, the
electrode can be formed by plating an electrode material or
depositing an electrode material in a high vacuum by electron beam
heating, or the like. The top surface electrode 15 formed of bus
bar electrodes 30 and finger electrodes 32 is commonly used as an
electrode on the light receiving top surface side of a photovoltaic
cell element, and a known method for forming a bus bar electrode
and a finger electrode on the light receiving top surface side of a
photovoltaic cell element can be applied.
[0094] In the exemplary embodiments above, a photovoltaic cell
element has a structure in which an n-type diffusion layer is
formed on the top surface of a semiconductor substrate and a
p.sup.+-type diffusion layer is formed on the back side, and a top
surface electrode and a back side electrode are provided on the
respective layers. However, it is also possible to produce a
back-contact type photovoltaic cell element by using the
composition for forming an n-type diffusion layer according to the
invention. A back-contact type photovoltaic cell element has all
electrodes at the back side in order to increase the area of the
light receiving surface. Namely, it is necessary to form both the
n-type diffusion region and the p.sup.+-type diffusion region at
the back side in order to form a pn-junction structure. Since the
composition for forming an n-type diffusion layer according to the
invention is capable of forming an n-type diffusion portion only at
a desired portion, it is suitably used for the production of a
back-contact type photovoltaic cell element. Although there is no
particular restriction on the shape or the size of a photovoltaic
cell element that is produced by the method for producing a
photovoltaic cell element as described above, it is preferably a
square having the size of from 125 mm to 156 mm at each side.
[0095] <Photovoltaic Cell>
[0096] The photovoltaic cell according to the invention includes
one or more photovoltaic cell elements produced by the production
method as mentioned above, and wiring materials that is positioned
on the electrodes of the photovoltaic cell elements. As necessary,
a photovoltaic cell may have a structure in which plural
photovoltaic cell elements are connected with a wiring material and
sealed with a sealing material. A photovoltaic cell element
produced by the production method of a photovoltaic cell element
can be used for producing a photovoltaic cell.
[0097] There is no particular restriction on the wiring material
and the sealing material, and an appropriate material may be
selected from materials that are commonly used in the industry.
Although there is no particular restriction on the shape or the
size of a photovoltaic cell, it is preferably from 0.5 m.sup.2 to 3
m.sup.2.
EXAMPLES
[0098] In the following, examples of the invention are described
more specifically. However, the invention is not limited to the
examples. Unless otherwise specified, reagent chemicals were used
for the chemicals. Unless otherwise specified, "%" means "% by
mass".
Example 1
[0099] A composition for forming an n-type diffusion layer in a
paste form was prepared by mixing 1 g of a
P.sub.2O.sub.5--SiO.sub.2--CaO glass (P.sub.2O.sub.5: 50%,
SiO.sub.2: 43%, CaO: 7%) powder, 0.3 g of ethyl cellulose, 8.6 g of
2-(2-butoxyethoxy)ethyl acetate, 0.1 g of an organic filler (PMMA
resin filler, MR grade, cross-linked particles, average particle
size: 0.1 .mu.m, degradation temperature: 400 C, manufactured by
Soken Chemical Engineering Co., Ltd.) The shear viscosity of the
composition for forming an n-type diffusion layer at 25 C was 500
Pas at a shear rate of 0.01/s, and 50 Pas at 10/s. The TI value was
1.00. The shear rate was measured at 25 C with a viscoelasticity
measuring apparatus (Rheometer MCR301, manufactured by Anton Paar
GmbH).
[0100] Next, the composition for forming an n-type diffusion layer
was applied by screen printing onto a surface of a p-type silicon
wafer (manufactured by PVG Solutions Inc.) in a shape of a fine
line, and dried on a hot plate at 150 C for 1 minute. A screen
printing plate designed for obtaining a 150 .mu.m-wide fine line
was used. The squeegee speed and the scraper speed were 300 mm/sec,
respectively, and the application amount was 2.1 g/m.sup.2. The
width of the fine line was measured with a light microscope
(manufactured by Olympus Corporation). The result was 180 .mu.m,
indicating that the expansion from the designed value was within 35
.mu.m.
[0101] Next, a thermal treatment was performed in a tunnel furnace
(horizontal tube diffusion furnace, ACCURON CQ-1200, made by
Hitachi Kokusai Electric Inc.) with an air flow of 5 L/min at 900 C
for 10 minutes. Thereafter, in order to remove a glass layer formed
on a surface of the p-type silicon substrate, the substrate was
immersed in a 2.5 mass % HF aqueous solution for 5 minutes, and
then subjected to washing with running water, ultrasonic cleaning,
and drying. A p-type silicon substrate on which an n-type diffusion
layer was formed was thus obtained.
[0102] The sheet resistance at a surface of the side applied with
the composition for forming an n-type diffusion layer was
40.OMEGA./.quadrature., and it was confirmed that an n-type
diffusion layer was formed by diffusion of P (phosphorus). The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed. The sheet resistance was
measured by a 4-pin probe method with a low resistivity meter
(LORESTA-EP model MCP-T360, manufactured by Mitsubishi Chemical
Corporation).
Example 2
[0103] A composition for forming an n-type diffusion layer in a
paste form was prepared in a similar manner to Example 1, except
that 1 g of P.sub.2O.sub.5--SiO.sub.2--CaO glass particles
(P.sub.2O.sub.5: 50%, SiO.sub.2: 43%, CaO: 7%), 0.3 g of ethyl
cellulose, 6.7 g of 2-(2-butoxyethoxy)ethyl acetate, and 2 g of an
organic filler (PMMA resin filler, MR grade, average particle size:
0.1 .mu.m, manufactured by Soken Chemical Engineering Co., Ltd.)
were used. The shear viscosity of the composition for forming an
n-type diffusion layer was measured by a similar method to Example
1. The results were 5000 Pas at a shear rate of 0.01/s and 80 Pas
at 10/s. The TI value was 1.80.
[0104] The composition for forming an n-type diffusion layer was
applied onto the p-type silicon wafer surface and dried by a
similar method to Example 1, and the line width was measured. The
line width was 155 .mu.m and the expansion from the designed width
was within 5 .mu.m. The application amount was 2.2 g/m.sup.2.
[0105] The p-type silicon wafer after application of the
composition for forming an n-type diffusion layer was subjected to
a thermal treatment by a similar method to Example 1, and the sheet
resistance was measured. The sheet resistance at a surface on the
side applied with the composition for forming an n-type diffusion
layer was 40.OMEGA./.quadrature., and it was confirmed that an
n-type diffusion layer was formed by diffusion of phosphorus. The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed.
Example 3
[0106] A composition for forming an n-type diffusion layer in a
paste form was prepared in a similar manner to Example 1, except
that an organic filler of the same kind having an average particles
size of 5.0 .mu.m was used instead of the organic filler having an
average particle size of 0.1 .mu.m. The shear viscosity of the
composition for forming an n-type diffusion layer was measured by a
similar method to Example 1. The results were 300 Pas at a shear
rate of 0.01/s and 60 Pas at 10/s. The TI value was 0.70.
[0107] The composition for forming an n-type diffusion layer was
applied onto the p-type silicon wafer surface and dried by a
similar method to Example 1, and the line width was measured. The
line width was 200 .mu.m and the expansion from the designed width
was within 50 .mu.m. The application amount was 2.1 g/m.sup.2.
[0108] The p-type silicon wafer after application of the
composition for forming an n-type diffusion layer was subjected to
a thermal treatment by a similar method to Example 1, and the sheet
resistance was measured. The sheet resistance at a surface on the
side applied with the composition for forming an n-type diffusion
layer was 40.OMEGA./.quadrature., and it was confirmed that an
n-type diffusion layer was formed by diffusion of phosphorus. The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed.
Example 4
[0109] A composition for forming an n-type diffusion layer in a
paste form was prepared in a similar manner to Example 1, except
that 1 g of P.sub.2O.sub.5--SiO.sub.2--CaO glass particles
(P.sub.2O.sub.5: 50%, SiO.sub.2: 43%, CaO: 7%), 8.3 g of
2-(2-butoxyethoxy)ethyl acetate, and 0.7 g of an organic filler
(PMMA resin filler, MR grade, particle size: 0.1 .mu.m,
manufactured by Soken Chemical Engineering Co., Ltd.) were used.
The shear viscosity of the composition for forming an n-type
diffusion layer was measured by a similar method to Example 1. The
results were 5000 Pas at a shear rate of 0.01/s and 80 Pas at 10/s.
The TI value was 1.80.
[0110] The composition for forming an n-type diffusion layer was
applied onto the p-type silicon wafer surface and dried by a
similar method to Example 1, and the line width was measured. The
line width was 155 .mu.m and the expansion from the designed width
was within 5 .mu.m. The application amount was 2.2 g/m.sup.2.
[0111] The p-type silicon wafer after application of the
composition for forming an n-type diffusion layer was subjected to
a thermal treatment by a similar method to Example 1, and the sheet
resistance was measured. The sheet resistance at a surface on the
side applied with the composition for forming an n-type diffusion
layer was 40.OMEGA./.quadrature., and it was confirmed that an
n-type diffusion layer was formed by diffusion of phosphorus. The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed.
Example 5
[0112] A composition for forming an n-type diffusion layer in a
paste form was prepared in a similar manner to Example 1, except
that 1 g of P.sub.2O.sub.5--SiO.sub.2--CaO glass particles, 0.29 g
of ethyl cellulose, 8.7 g of 2-(2-butoxyethoxy)ethyl acetate, and
0.01 g of an organic filler (PMMA resin filler, MR grade, average
particle size: 0.1 .mu.m, manufactured by Soken Chemical
Engineering Co., Ltd.) were used. The shear viscosity of the
composition for forming an n-type diffusion layer was measured by a
similar method to Example 1. The results were 260 Pas at a shear
rate of 0.01/s and 80 Pas at 10/s. The TI value was 0.51.
[0113] The composition for forming an n-type diffusion layer was
applied onto the p-type silicon wafer surface and dried by a
similar method to Example 1, and line width was measured. The line
width was 220 .mu.m and the expansion from the designed width was
70 .mu.m. The application amount was 2.3 g/m.sup.2.
[0114] The p-type silicon wafer after application of the
composition for forming an n-type diffusion layer was subjected to
a thermal treatment by a similar method to Example 1, and the sheet
resistance was measured. The sheet resistance at a surface on the
side applied with the composition for forming an n-type diffusion
layer was 40.OMEGA./.quadrature., and it was confirmed that an
n-type diffusion layer was formed by diffusion of phosphorus. The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed.
Comparative Example 1
[0115] A composition for forming an n-type diffusion layer in a
paste form was prepared by mixing 1 g of
P.sub.2O.sub.5--SiO.sub.2--CaO glass particles (P.sub.2O.sub.5:
50%, SiO.sub.2: 43%, CaO: 7%), 0.68 g of ethyl cellulose, and 8.32
g 2-(2-butoxyethoxy)ethyl acetate, without adding an organic
filler. The shear viscosity of the composition for forming an
n-type diffusion layer was measured by a similar method to Example
1. The results were 200 Pas at a shear rate of 0.01/s and 80 Pas at
10/s, which were not significantly different. The TI value was as
low as 0.40.
[0116] The composition for forming an n-type diffusion layer was
applied onto the p-type silicon wafer surface and dried by a
similar method to Example 1, and the line width was measured. The
line width was 270 .mu.m and the expansion from the designed width
was 120 .mu.m. The application amount was 2.3 g/m.sup.2.
[0117] The p-type silicon wafer after application of the
composition for forming an n-type diffusion layer was subjected to
a thermal treatment by a similar method to Example 1, and the sheet
resistance was measured. The sheet resistance at a surface on the
side applied with the composition for forming an n-type diffusion
layer was 40.OMEGA./.quadrature., and it was confirmed that an
n-type diffusion layer was formed by diffusion of phosphorus. The
sheet resistance at the back side was unmeasurable, namely
1000000.OMEGA./.quadrature. or more, and it was confirmed that an
n-type diffusion layer was not formed.
[0118] The measurement results of Examples 1 to 5 and Comparative
Example 1 are shown in Table 1.
TABLE-US-00001 Comparative Example 1 Example 2 Example 3 Example 4
Example 5 Example 1 P.sub.2O.sub.5--SiO.sub.2--CaO Glass particles
1.0 1.0 1.0 1.0 1.0 1.0 Ethyl cellulose 0.3 0.3 0.3 -- 0.29 0.68
2-(2-Butoxyethoxy)ethyl acetate 8.6 6.7 8.6 8.3 8.7 8.32 Organic
filler PMMA (0.1 .mu.m) 0.1 2.0 -- 0.7 0.01 -- PMMA (5.0 .mu.m) --
-- 0.1 -- -- -- Shear viscosity Shear rate 10/s 50 80 60 80 80 80
(Pa s) 25 C. Shear rate 0.01/s 500 5,000 300 5,000 260 200 TI value
1.00 1.80 0.70 1.80 0.51 0.40 Expansion in line width (.mu.m) 30 5
50 5 70 120 [150 .mu.m screen printing plate] Top surface sheet
resistance (.OMEGA./.quadrature.) 40 40 40 40 40 40 Back side sheet
resistance (.OMEGA./.quadrature.) 10.sup.6 or more 10.sup.6 or more
10.sup.6 or more 10.sup.6 or more 10.sup.6 or more 10.sup.6 or
more
[0119] In Examples 1 to 5, in which a composition for forming an
n-type diffusion layer of the invention includes a compound
containing a donor element, a dispersing medium, and an organic
filler, exhibit a suppressed expansion in line width as compared
with Comparative Example 1. This indicates that a fine line pattern
can be formed in a more favorable manner in Examples 1 to 5. Among
Examples 1 to 5, Example 2 and Example 4, in which the amount of an
organic filler is relatively greater, expansion in line width is
more suppressed. This is presumed to be because the shear viscosity
at a low shear rate is relatively higher, and an ability or
retaining the line width is relatively greater than the other
Examples.
[0120] The entire contents of the disclosures by Japanese Patent
Application No. 2012-037384 are incorporated herein by reference.
All the literature, patent literature, and technical standards
cited herein are also herein incorporated by reference to the same
extent as provided for specifically and severally with respect to
an individual literature, patent literature, and technical standard
to the effect that the same should be so incorporated by
reference.
* * * * *